U.S. Provisional Application No. 61/384,966, filed Sep. 21, 2010, is incorporated herein by reference in its entirety.
Machine tools and machining centers, hereinafter sometimes jointly referred to by the term “machine tool”, including, but not limited to, milling machines and the like, include rotatable spindles configured for holding tools such as milling cutters, drills, reamers, and the like, for performing machining operations, such as but not limited to, milling, drilling, boring, and reaming. Such tools are typically removably held in the spindle by tool holders, which allow quickly changing the tools, for instance, by an automatic tool changing apparatus. Honing is a machining operation that can impart a much more precise size, shape, and finish to work piece bores, but many traditional honing tools require a feed mechanism or system for adjusting a feed position and/or feed force of honing elements, e.g., abrasive stones, of the tool, in process, as those elements are urged against the surface of a bore of a work piece for honing the bore. Known machine tools and machining centers lack the required feed system or mechanism, and thus the traditional in process adjustable feed honing tools have not been used on machine tools. But many machine tools and machining centers have through-the-spindle coolant delivery systems operable for directing a flow of liquid coolant from a port or orifice in the spindle, into a mating port or orifice of a tool holder held by the spindle.
There exist several honing tools designed for use in machine tools that utilize through-the-spindle coolant pressure to directly or indirectly force the abrasive stones of the honing tool into the surface of the bore. Reference in this regard, Hyatt, et al. U.S. Pat. No. 5,800,252, which describes a honing tool designed for use in a machine tool having through-the-spindle coolant. In the Hyatt, et al. tool, by means of passages the coolant pressure is supplied directly to chambers under the abrasive stones providing direct force. However, an observed shortcoming is that this type of tool allows each abrasive stone to feed independently which will not reliably improve the roundness of a bore, which is often a goal of the honing process. Usually, roundness is accomplished by having abrasive stones fed by a single wedge that keeps all stones advancing and retracting in unison.
U.S. Pat. No. 6,739,949 B2, Becksvoort, et al. and U.S. Pat. No. 7,070,491 B2, Becksvoort et al, both describe a honing tool with a wedge that is fed by the pressure of coolant delivered through the machine tool spindle. Both of these tools, however, rely on an internal helical spring to retract the tool. Spring force naturally is increased as the abrasive stones are fed outward. The net force delivered to the wedge is the coolant force minus the spring force. This results in a variation of the feeding force supplied to the wedge. Although in theory this could be compensated for by adjusting the coolant pressure, a reliable feedback loop would be required to do so, and in absence of such a feedback loop the feed force will be diminishing over time as the abrasive stones wear. Even during the travel of a single honing cycle the net feed force will drop as the wedge feeds against the retraction spring.
As an additional limitation, none of the known prior art discussed above includes a means to detect when the honing operation has achieved the desired bore size. Honing is typically performed for a set period of time, or some external means of in-process bore gauging must be employed.
As another observed limitation, none of the above referenced prior art discloses a manner of using traditional in-process adjustable feed honing tools on the spindle of a machine tool or machining center.
Thus, what is sought is a honing tool holder that provides a capability for automatically feeding the honing elements or stones when in the bore of a work piece, and for automatically stopping the feeding when a particular condition such as a bore size, is reached, to enable use of an in-process adjustable feed honing tool in a machine tool, machining center, or the like, lacking a feed mechanism or system, but including a through-the-spindle coolant delivery system.